Chemical composition of snow cover on the western Swiss Alps

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1 Hydrlgy in Muntainus Regins. I - Hydrlgical Measurements; the Water Cycle (Prceedings f tw Lausanne Sympsia, August 99). IAHS Publ. n. 93, 99. Chemical cmpsitin f snw cver n the western Swiss Alps Aurèle PARRIAU & Jean-Daniel DUBIS Federal Institute f Technlgy, Labratry f Gelgy, 5 Lausanne, Switzerland Martial DRAY Centre de recherches gédynamiques, Université Pierre et Marie Curie, Thnn les Bains, France ABSTRACT The AQUITYP prject studies the gechemical imprint given t the water by the aquifers thrugh which it has passed. A cmplete analysis f the utput f flw systems has been analyzed, yielding the majr and minr mineral cmpnents. The interpretatin f the rle f the undergrund envirnment implies a knwledge f the cmpsitin f the input, especially fr aquifers which have lw reactivity with grundwater. In this case, pririty has been given t accessing the cmpsitin f recharge grundwater in muntainus regins. The amunt f snw accumulated befre the spring thaw is a practical methd f determining the cmpsitin f the winter depsits. A netwrk f 4 pints was established at the end f the winter seasn. These pints are distributed in varius reginal prfiles at altitudes between and 4 m. The labratry analyses shw a variability f parameters mainly accrding t the distance frm urban znes.. PRINCIPAL AIMS The study f the cmpsitin f snw accumulatin in the Alps is linked t the AQUITYP prject, which was started several years ag t study systematically the typlgy f aquifers (Parriaux S Lutz, 988, Parriaux S Dubis, 99). The principal aims can be summarized in the fllwing manner: a) Quality f grundwater recharge: The study f the gechemical regime at the utput f a typical aquifer necessitates infrmatin cncerning the cmpsitin f the surface water. This is even mre imprtant when the grundwater is slightly mineralized (Dubis S Parriaux, 99) and when an analysis f the trace cmpnents is carried ut. The istpic cmpsitin is als imprtant. This subject is treated in a secnd article (Dray et al., 99) in these prceedings. b) Chemical image f precipitatin in muntainus regins: Even thugh the "Snw cver" netwrk was nt cnceived with this aim in mind, it enables an average image f the spatial dispersin f the snw cmpsitin during the winter perid. The dispersin f natural mineral substances, as well as thse linked t human activity at the ft f the muntain chains, is described. This image des nt pretend t treat the time variability at the scale f pluvimétrie events, as this wuld necessitate a different sampling cncept which wuld becme much t cmplicated in the framewrk f this prject. 5

2 Aurele Partiaux et al BSERVATIN NETWRK The mesh was made up f 4 pints distributed in and arund the Alpine catchment basin f the AQUITYP netwrk. These pints were situated in the Prealps and the west Swiss Alps, in the interir f the Rhne basin and n its edge. Their altitudes varied between 33 and 48 m. Generally, they were gruped by increasing altitude in transversal frmatin, as is shwn by the Mnt Blanc and Pennic Alps prfiles (Fig. and Table ). The number f pints is limited by the cst f ne day f helicpter time per year. The present article analyzes the results f snw accumulated during the winter seasn. Thse f the seasn are still underging analysis. LEGEN : ) N Reference line fr the ft f the chain '83 Altitude (msm) Statins Crdinates, Y Statins Crdinates, Y FIG. & TABLE Situatin f the sampling statins f the snw cver,

3 3. SAMPLING TECHNIQUE 53 Chemical cmpsitin f snw cver n the western Swiss Alps Sampling by helicpter has the advantage f being able t insure synchrnized samples (in ne day) f relatively inaccessible regins. Hwever, this must be carried ut rapidly fr financial reasns. The sampling prcess was the fllwing: Standard scenari: a) Nn-tubed bring with an auger (4 mm in diameter,.7 m maximum depth) b) Placement f the snw sample in a plastic (PVC) case c) Mixing f the sample fr hmgenizatin d) Filling f plyethylene bttles with the "average snw" e) Slw melting in the labratry, fllwed by analysis Stratificatin scenari: Identical t the standard scenari except the sampling was carried ut by 25 t 35 cm runs. Three parallel brings were executed at.5 m frm each ther in rder t btain enugh snw. 4. ANALYSES The samples were analyzed accrding t classical methds f mineral hydr-chemistry: emissin and atmic absrptin spectrmetry, graphite furnace, inic chrmatgraphy. A prcess f in cncentratin n a 8-hydrxyquinline resin was necessary due t the weak mineral cntent f the snw. 5. RESULTS The analytical results have been synthesized and are presented n maps f spatial distributin fr each parameter (Fig. 2). Their interpretatin is carried ut as a functin f the fixed gals (Chap. ). 5. Grundwater recharge The gechemical cmparisn f the water frm snw with that f grundwater fund in crystalline massifs is meaningful. Figure 3 shws that the gechemical input f the precipitatins is ttally negligible fr the majr catins. Hwever, a large number f anins is already present in the recharge water in quantities f percents fr the sulfates and f several tens f percents fr the nitrates and especially the chlrides. n the basis f the majr cmpnents, it can be cncluded that the water-rck interactin is predminant. Further trace analysis f the grundwater will verify if this cnclusin is valid fr the minr cmpnents as well. 5.2 Chemical image f the precipitatins Table 2 regrups the average parameters analyzed as well as their variability in the bservatin netwrk. These values are cmpared t thse fund in the literature fr similar sites.

4 Aurele Partiaux et al. 54 Q I u Q CL l> ri cr. u CRD. Q CE m, - 2-»U 2 ~\ "r s\ TDS (ppm) SI i* A 2 ' 8.-5 / ^ V\ * >-4l.3 ^/".8., a ' <>.4* -\%.6 *. -6 -S, _7 l. 3 *l * 3. 3A"- -» i km f.8 \\ 7 \l.2.5 \." ^<S ij^-, \K 392 A29*'..r.2 2 " U - b, M Il " tw *.* i C/ T 2 m \s \ r-^ \ ^<348 S I/.269.« Il 3? «-,.2. V.6.. " S ^... C Mn «". Q *. Zn ue^-. U, \\ T " \ \.. I/ \ **, <a n l ^. \-^..... ^. ~ < " ',. *.*_» fil CRD. Y A.2 4.3* st *».. ti si ^ t/.7** 3 " V * H 4Bl. «V'>.6. :! il..987 I V58 \l' Il Vç^ ï.l PW Il " m K Il m ^ s,* si 6 5. N 3 (ppb; Il S «I* , 7» Il \ Fe Si ^* 5-8 Il Q, s,. «M CRD. Y ' 7. 27* '" i M / 2 * «I i "' y \ ' \ 2 H \ * b "I *l \ " " <6 A/ Il " tw * * Ca Il " V? 2 / / ""' ' * ' *8 Si U^. /.2 r 3 Q t ' 7 Si 2 SI - S '_2 I,.4. \,6.6 } } ab * Cu " ^2 tw Si*- SI * V.3.7 "*&2. - * Pf> *-*!. si CRD. Y m.. * FIG. 2 Spatial parameters. variability f the physic-chemical

5 55 Chemical cmpsitin f snw cver n the western Swiss Alps.8 FIG. 3 Cmparisn f cncentratins f majr ins in a grundwater f Mnt-Blanc massif and in a snw sample. TABLE 2 Average and variability f physic-chemical parameters. TDS (ppm) a, a SB Mg K Ca CI N3 I a. Mn Fe CU Zn Cd Pb s x min C ^max Analyses carried ut in the French and Austrian Alps (Page, 987) give cmparable rders f magnitude fr the majr catins. Their variability with time is increased by taking int accunt varius snw events f the seasn. The cmparisn with the analyses in the Mnt Blanc massif (Batifl and Butrn, 984) is mre cmplex. verall, the cncentratins btained in ur study are t times less, with the exceptin f calcium, manganese, cpper and cadmium. The reasn fr these differences can prbably be fund in the treatment f the sample with nitric and flurhydic acid that these authrs used, which tends t put the elian particles in the accumulated snw in slutin. Spatial arrangement: Generally speaking, the cncentratins f the parameters seem t be influenced by the altitude as well as by the distance frm urban and industrial znes. Zning by altitude: The graphical representatins f the different parameters (Fig. 4) shw a vague negative crrelatin between the cncentratins and altitude. These distributins can be separated int tw grups : a dmain belw 28 m where the values are dispersed withut any clear pattern, a dmain at high altitude where the cncentratins are lw.

6 Aurèle Parriaux et al. 56 Zning accrding t distance frm urban regins: The situatin at each pint is represented with respect t the large urban regin fund n the Swiss plateau, situated t the NW f the investigatin area. A reference line with a N45E azimuth was selected as the schematic brder f this regin. A value was then assigned t each statin, crrespnding t the distance frm this ppulated area. The behaviur f varius parameters accrding t this distance is given in Figure 5. The majrity f the fllwing cncentratins appear t be rather distinctly negatively crrelated with distance: TDS (Ttal Disslved Slid), Na, CI, N 3, S 4, Mn, Cu, Zn, Cd and Pb, even thugh the crrelatin cefficient is lw. An imprvement f the crrelatin can be bserved n certain graphs f Figure 5 if the urbanizatin f the Rhne valley is taken int accunt. This is the case fr Mn, Cu, Cd, Pb with statin numbers and 2, which are clse t the industrial znes f the lwer Rhne in the Valais cantn. T access.the rigin f these cmpnents, the example f the NaCl-HCl cuple was examined: NaCl: natural meteric rigin, HC: essentially anthrpgenic rigin. The cncentratin f Na + and Cl~ clearly shws that fr meq. f sdium, there exists apprximately meq. f chlrides. It can be cncluded that in this case, abut 9% f the mineral charge cmes frm human activity. These bservatins indicate that the cncentratins f the principal cmpnents depend directly n the distance frm the majr centers f pllutant emissins. The relatins bserved as a functin f altitude (Fig. 4) are therefre illusry, as high-altitude znes are als far frm human activity. 6. DISCUSSIN F THE RESULTS The results btained must be reviewed t evaluate varius causes which may have altered the quality f the measurements. Cntaminatin : Chemical influence f the sampling instruments n the snw. Snw-sil chemical exchanges at the base f the snw layer. Accidental cntaminatin in the labratry. The behaviur f pints 4 and culd be linked t cntaminatin. Time dependent representativity: The samples d nt reflect the entire snw accumulatin during the winter seasn fr the fllwing reasns: nly 4 samples include measurements frm the cmplete snw layer. Fr the thers, the prfile is incmplete and the first snws'are missing. - An imprtant snw event ccurred after the samples were taken (secnd half f March). Spatial representativity: The pints were chsen n prfiles with altitudes crrespnding t the basins studied in the AQUITYP prject. They were fund t be in extremely varying mrphlgical cnditins. This means that there were great climatic differences during snwfalls. Elian transprt f the snw n the grund tends t increase

7 I "i I I i i i i i i I 57 Chemical cmpsitin f snw cver n the western Swiss Alps 9" <r>ct e- in cns" m l"! f I I I V I I I. -8 ÇZ en,_ NT C %T I i i i if I"I i i? n *» 2 _UD Q.. es. v^, ~- Q, C -a- [ II I I I M ) II I S 2 l,( -Q - Q. in Q. <^*w -S5 -a -Q - CL I I I I I II I I I I I G S * -- I I I I I I I I I I I I I I u> vt "~ ti "*""d Q. a. ID-Q -c'a <45 f- I I I I [ II I I I IT _ U <" I I II I M I I I II,- *~ a - -8 I I I I I I I I I 'c> <= C> I i iiii it i i i 3CL I I I I I I II I I I I I I - CL D l-c h8 &.' <r w" i i i i I i i i i i i i»6 ":; : CL >. M I I I I I I I I I I I ( "J ) aruinv I I I I I l"l * I I - 2! m i-si?. a I I I I I I I I I I I cs ( UJ ) aruinv w ) 3ruinv

8 Aurèle Partiaux et al. 58 t- p Cn I I I I en es c- u> î 3" sï "" % ( " (N n I I I I! ci i i i i l i T i f,,,.,.. s (M CQ. in Q. in _ - 3-Q «3 3= 3Q.. i r- () n i r i i n i r i r - _ i i i i n n r I I I l l I " a y-m ; : s «"> c> 2: rsi Ci -8 '-8 k8û 3 U3 3 U5 ^ c en.? -Jin *4 m s i r -j ut t I C - ï 3t *- I I j ~ -. TT I I C *~ _ ( C m < c K ~ C f,,, ~ i,,. ~ N I i i i i i i r " " I I I I I I I minin ininin l/>fc>lf>c>tfitf-> ( UJH) a ( w>n a il il i ri il _.Ôinm ir> <bu. ( m ) a S

9 59 Chemical cmpsitin f snw cver n the western Swiss Alps this variability, as the stable istpes f the same regin seem t indicate (Dray et al., 99). In spite f these limitatins, the results fllw certain rules, especially the crrelatin with znes f pllutant emissins. 7. CNCLUSINS The tw main gals f the study were realized:. Infiltratin water resulting frm snw thaw has a weak mineral cntent (majr cmpnents), very inferir t that f grundwater, even in the crystalline massifs. Therefre, a systematic bias des nt seem t exist in the gechemical interpretatin f grundwater. Trace studies remain t be carried ut. 2. The spatial distributin f the cmpnents shws that they are principally f anthrpgenic rigin and that their cncentratin is linked t znes f human activity. The samples frm the seasn are still underging analysis and this analysis shuld prvide the infrmatin necessary t cmplete these first bservatins. ACKNWLEDGMENTS g t the Swiss Army fr having prvided us with the necessary helicpter transprt, withut which this study wuld nt have been pssible. Als, we thank the GELEP persnnel fr the analyses and the layut f the article. REFERENCES Batifl, F.M. & Butrn, C.F. (984) Atmspheric heavy metal in high altitude surface snws frm Mnt Blanc, French Alps. Atmspheric Envirnment, S./, Dray, M., Parriaux Aurèle & Dubis Jean-Daniel (99) Image synchrne de la cmpsitin istpique de la cuverture neigeuse des Alpes de Suisse ccidentale. Prc. & reprts IAHS Cnf. f Lausanne 99. Dubis, J.D. & Parriaux, A. (99) Spatial and time-dependent variatins f the springs f crystalline aquifers f the Mt.Blanc and Aguilles Ruges massif (Switzerland, France and Italy): first results. Prc. f 22nd IAH Cngress Lausanne 99. Page, Y. (987) Meterlgy, chemistry, acidity f muntain snwfalls and snwpack chemistry. Jurnal de physique. Cllque CI, Tme 48. Page, Y. (987) The chemical evlutin f a seasnal snwcver at midland-high altitude. In: H.G. Jnes & W.J. rville-thmas (Eds) Seasnal snwcvers: Physics, chemistry, hydrlgy, Parriaux, A., Lutz, T. (988) Cntributin f an infrmatized cncept t the chemical analysis f grundwater series. Prc f 2st IAH Cngress in Guilin fchina). Parriaux, A. (99) The AQUITYP prject: twards typlgy f aquifers in the alpine rgen. Prc. f 22nd IAH Cngress Lausanne 99. Parriaux, A. & DUBIS, J.D. (99) Grundwater typlgy befre and after the intrductin f the ICP-MS. Chimia. Birkhàuser AG, Basel.

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